Tuesday, December 25, 2012

797B Off-Highway Truck: Sensors

Sensors provide information to ECM input(s) about changing conditions. The ECM receives the following types of information: speed, temperature and position. The sensor signal changes in a proportional manner in order to reflect the changing condition. The ECM sends the information from the speed sensor to the gauges. The operator can view the information from the speed sensor on the gauges. The ECM recognizes two types of sensor signals.

Frequency - The sensor produces an AC signal. The AC signal frequency (Hz) varies as the condition changes.

Pulse width modulated (PWM) - The sensor produces a digital signal. The duty cycle of the digital signal varies as the condition changes and the frequency of the digital signal is constant.

Position Sensor (Hoist Lever)

The hoist lever position sensor produces a signal that varies the duty cycle as the lever position changes.

The hoist lever position sensor is an input to the ECM. The hoist lever position sensor connects to connector contact J1-51. The sensor tells the ECM about the operator's request for activity from the hoist. The ECM activates the appropriate solenoids. There are several override functions and safety measures with the hoist system. See Systems Operation, "Hoist System Function" for more information.

The sensor has a connector with three contacts. The sensor receives electrical power on pin "+V" from the battery. The sensor ground is connected to the ECM through pin J1-12. The sensor signal is connected to the ECM through pin J1-51.

The ECM records diagnostic codes that occur with the sensor signal as a CID 0773 diagnostic code. This diagnostic code is recorded. This may cause the ECM to ignore requests for any additional hoists.

Sensor Buffer (Body Position)

The body position sensor is an input to the ECM. The sensor connects to connector contact J1-25. The position sensor tells the ECM the position of the body.

The sensor has a connector with three contacts. Contact "A" receives the electrical power from the battery. Contact "B" is connected to sensor ground through pin J1-12. Contact "C" is connected to the ECM through pin J1-25.

The ECM records diagnostic codes that occur with the sensor as a CID 1175.

Shift Lever Position Sensor

Position Sensor (Shift Lever)

Table 1
Shift Lever Position Logic
Gear	Ground Verify	5	4	3	2	1
	J1-29	J1-28	J1-39	J1-38	J1-37	J1-36
1R	G	G	O	O	O	O
N	G	G	O	G	O	O
1F	G	G	O	O	G	O
2F	G	G	O	O	O	G
3F	G	O	G	G	O	O
4F	G	O	G	O	G	O
5F	G	O	G	O	O	G
6F	G	O	O	G	G	O
7F	G	O	O	G	O	G

The shift lever sensor is an input of the ECM. The sensor connects to contacts J1-28, J1-29, J1-36, J1-37, J1-38, and J1-39. The sensor tells the ECM the operator's highest desired gear. The shift lever is connected mechanically to the shift lever in the shift console. The sensor has a connector with ten contacts.

Five contacts on the sensor provide the ECM with the information for the position of the shift lever. For each position of the shift lever, the sensor grounds two of the five contacts through internal diodes. The sensor opens the other three contacts. The ECM interprets the status of the five contacts.

Contact 1 of the sensor provides the ECM with a ground verify signal. The contact is normally connected to ground at all times. This tells the ECM that the sensor is connected. This prevents the ECM from thinking that the switch is missing when the switch is between gears.

Contact 2 is connected to frame ground. Contact 10 provides a neutral signal to other devices in some applications. Contact 6 is connected to + battery voltage. Contact 7 is blank. This contact serves as an index for the mating connector.

The ECM records diagnostic codes with the sensor as a CID 0702 diagnostic code.